1. Field of the Invention
The field of the invention is acoustical coupling devices for ultrasound scanning of the human breast.
2. Description of the Prior Art
When applying ultrasonic visualization instrumentation, it is typically necessary to use a coupling agent between the transducer emitting the high frequency sound wave and the skin surface of the patient. The coupling medium acts as a transport medium for the sound waves and should match as closely as possible, the acoustic impedance of the skin. Liquids, and in particular, water are typically used as coupling agents because of their ready availability and acoustic properties.
Breast scanning has been performed with the use of an indirect coupling agent such as a "water bag". In this type of technique a so called "bag" (a flexible container which molds to the skin surface) of water is placed against the breast of the patient and the transducer is placed or permanently located within either an open or closed water bag. There are several disadvantages of the standard water bag technique in relation to its use with ultrasound breast scanning. These disadvantages include (1) the trapping of air between the bag surface and the skin which impedes the transmission of the sound waves; (2) potential failure of tumor detection due to displacement of the tumor mass from its original position caused by pressure of the water bag; (3) inability to verify tumor location by manually palpating the breast; and (4) potential failure to detect subtle alterations in structural components of the breast tissue (which are the earliest sign of breast cancer) because of alterations in the structural architecture resulting from the "water bag" pressure.
Devices are currently being used which provide for direct water coupling of the human breast with the patient in either a prone or a sitting forward position. In these techniques, the breast is allowed to float in the liquid environment and thus inaccuracies due to pressures caused by a water bag are alleviated. However, the techniques of direct water coupling with the patient in a sitting forward or prone position present a disadvantage in that during the scanning procedure the breast area is not readily accessible to a technician and thus repalpation of the breast and the making of fine adjustments in the scan are difficult and awkward to perform. U.S. Pat. No. 3,480,002 to Flaherty et al. discloses the above mentioned ultrasound scanning techniques of using a water bag and of utilizing direct water coupling for an ultrasound scan performed with the patient in a prone position.